Doping effect for ionic conductivity in DNA film

We have investigated the role of ions such as H+ and Rb+ in the electrical conductivity of DNA films. On the basis of the relative humidity dependence of electrical conductivity, the electrical conductivity of DNA films is found to strongly depend on relative humidity h and its dependence comprises three regions: (I: h < 17%), (II: 17% < h < 59%), and (III: h > 59%). Moreover, the 1H-NMR absorption line becomes narrow in regions (II) and (III) due to the appearance of mobile protons. These results indicate that mobile protons play an important role in the electrical conductivity in regions (II) and (III). Furthermore, based on these results, it is deduced that the electrical conductivity in region (II) is caused by proton hopping from one PO4 tetrahedron to another accompanied by the breaking and rearrangement of the hydrogen bond. In addition, we have also observed that the electrical conductivity increases by doping rubidium ions into DNA film.